In the present description, by “biological material” is meant a biological tissue, a preparation or an extract originating from biological tissue, liquid or solid, or a medium, natural or not, capable of containing bacteria, for example flowing water or water for rinsing fruits and vegetables. Such a material can also be a mixture of at least two materials as defined above; it can therefore be, in particular, either prepared from tissues, organs, stools or body fluids from a patient suffering from a disease, or obtained from “in vitro” cultures; such biological material can be also a serum, plasma, urine, cerebrospinal fluid, synovial fluid, peritoneal fluid, pleural fluid, seminal fluid or acetic fluid.
A plasma glycoprotein called β2-glycoprotein I, or also abbreviated to “β2GPI”, has already been described; the sequence of this human glycoprotein has in particular been referred to in the articles by J. LOZIER et al., Proc. Natl. Acad. Sci. ISA, Vol. 81, p. 3640-3644 (July 1984), and by T. KRISTENSEN et al., FEBS Letters, Vol. 289, p. 183-186 (1991). It has been noted that this β2GPI protein exhibits polymorphism: the name β2GPI is considered hereafter as generic for all forms.
In the international application WO 94/18569, it was pointed out that certain, in particular proteinaceous, infectious compounds bound to the form of β2GPI which had been described in French patent 2 701 263. In the document WO 94/18569, a method for detection and/or assay of viral compounds is proposed, in which the infectious viral compounds are bound to the form of β2GPI used; therefore this form of β2GPI is added to infectious viral compounds contained in a biological material, so as to separate the viral compounds thus captured in order to then detect them and/or assay them. In European patent EP 775 315, the formation of a complex between an infectious, in particular proteinaceous, compound and any form of β2GPI is described; the infectious compound could, in particular, be a bacterium. It is clear from these documents that the β2GPI is capable of binding to a flat solid support, such as the bottom of wells in a microtitration plate, and that the β2GPI thus adhering to this flat solid support, is capable of binding bacteria present in clinical, biological or environmental samples at very low concentrations. It is known, moreover, that such samples can contain substances inhibiting, at least partially, the detection of pathogens, substances which, as a result, can reduce the sensitivity of the detection. It is therefore important to be able to capture and concentrate these pathogens in order to eliminate the substances which inhibit their detection.
The studies of the Applicant company have shown that the binding of the β2GPI to the bottom of the wells in the titration plates, took place thanks to a particular conformation of the β2GPI, a conformation which subsequently allowed the formation of a complex of the β2GPI with an infectious compound. The literature had moreover reported that the conformation of the β2GPI varied at its binding to a solid surface (Matsuura et al., J. Exp. Med. 179, p. 457-462 (1994)). A method for the concentration of viruses had already been described (A. IWATA et al., Biol. Pharm. Bull. 26(8), p. 1065-1069 (2003)), using sulphonated magnetic microbeads to which the viruses would adhere, the concentration of the viruses being obtained due to the fact that the microbeads were magnetic and could be separated from the infectious medium by the action of a magnetic field. Unfortunately, the result of this technique was essentially a function of the adhesion of the viruses to the microbeads. This document explains in detail that certain non-enveloped viruses do not bind to beads made of polyethylene-imine and that it is necessary to use sulphonated microbeads in order to concentrate certain viruses. Moreover, for certain viruses, it was necessary to add bivalent cations. It follows from this finding that, depending on the nature of the virus, the polymer constituting the microbeads must be different, grafted or not grafted, and that bivalent ions are necessary or not necessary; the beads must therefore be prepared on an ad hoc basis depending on the virus to be concentrated. The same findings emerge from the document by E. UCHIDA et al., Journal of Virological Methods, 143, p. 95-103 (2007), which relates to the concentration of the human hepatitis A, B, and C viruses. In the presence of a sample containing an unidentified virus to be detected, it is not possible to determine what kind of microbeads is capable of giving rise to an adhesion of the virus of interest.